The present invention relates to a PWM (Pulse Width Modulation) circuit of programmable subframe system and, in particular, to a PWM circuit of programmable subframe system that divides a frame into subframes to suit for modulation.
There are two conventional PWM methods, which are one Frame Method and Subframe Method of fixed number.
As shown in FIG. 8, an example of one Frame Method is the method which a counter counts up the input clocks and resets the PWM output when the value of data register becomes same to the value of the counter and repeats the setting of PWM output with overflow of the counter and varies the duty of PWM output according to the value of the data register.
The subframe method of fixed number is a method to modulate and output pulse width corresponding to the value of data register with dividing into several subframes.
Digital/Analog conversion can be mentioned as an example of application of PWM, and it is described in U.S. Pat. No. 4,567,468 filed by Japan Sharp (patented in Japan as JPN 59055623).
Because the conventional PWM method uses the One Frame Method or Subframe Method of fixed number, it has the defect to limit the output formation and then application extent.